Flat conductor cable (FCC) underlying carpet tiles is in present use to supply electrical power to various points of use, as for example, handling task lighting and appliance loads in commercial buildings. The flat conductor cable includes in a common form thereof a plurality of flat conductors i.e., live, neutral and grounding conductors encased in a plastic electrically insulative casing and additionally having a metallic shield disposed at the upper surface of the cable. A layer typically made of tough insulation material is provided on the bottom of the cable as an abrasion protection shield. The metallic shield is electrically grounded to provide against electrical hazard such as accidental piercing of the shield and the live conductor by an object. An advantage of the use of this type of conductor cable is the facility with which it can be installed beneath carpeting and carpet tiles while at the same time allowing for transfer of power therefrom at selected locations, pedestals or transfer receptacles being installed for such purpose.
Various specialized types of devices including receptacles are known for establishing power take-off from the flat conductor cable at a given location. Thus, for connecting a receptacle at a desired location, a terminal block carrying insulation piercing members or contacts can be secured over the flat conductor cable with the contacts piercing the flat conductor cable to establish continuity with the respective cable conductors. A receptacle can then be placed over the terminal block with suitable connection between the terminals of the block and contact points in the receptacle being made with round wire connectors. With such installation the cable run can be terminated at the take-off location or it may pass through the terminal block so that additional receptacles can be connected further down the line. It is also known to use for purposes of providing power take-off, a receptacle which embodies insulation piercing contacts therein and employed when installed directly over a conductor cable to have these piercing contacts electrically connectively engage the conductors in the cable.
One of the drawbacks of utilizing the types of devices described above for providing power take-off from a flat conductor cable is the difficulty of insuring positive and effectual maintenance of electrically conductive contact between the flat cable grounding conductor and the associated insulation piercing grounding contact in the terminal block if such is used, or between the cable grounding conductor and the associated insulation piercing grounding contact carried in the receptacle if that type of device is used directly on the cable. It is equally important to insure proper electrical contact between the grounding contact and any metallic grounding shield covering the cable. These prior art devices, be they terminal block or receptacle types produce contact between the insulation piercing contacts and the flat conductor cable conductors and any protective shield by pressure imparted from the terminal block in the one case or the receptacle body in the other, the pressure resulting from the tightening of fastening screws passing directly through the receptacle or fastening screws used to secure a base plate to the floor, which base plate in turn is used to clamp the terminal block securely in place over the flat conductor cable. Since it is commonplace to make the receptacle and the terminal blocks as one piece structures, and since it is commonplace to effect fastening at the ends thereof which are in regions immediately adjacent the flat conductor cable live and neutral conductors, such fastening can influence the degree of proper contact between the terminal block grounding conductor associated contacts or the receptacle grounding conductor associated contacts. Such influence is in spite of the fact that a further separate fastener may be used at a location centrally of the terminal block or receptacle, the region wherein the grounding contacts usually are carried in the terminal block or the receptacle. In fastening or clamping of prior terminal blocks or receptacles it is believed that such can produce a stress/strain condition in these structures causing them to bow upwardly slightly in the center and hence lessening the downward pressure imparted to the grounding contact at that location. Tightening of any centrally located fastening screw it is thought can be resisted by such a stress/strain condition sufficiently to impair the positive electrically conductive contact which should exist with respect to and between the receptacle or terminal block insulation piercing grounding contact on the one hand, and the cable grounding conductor and shield on the other.